The present invention relates to a method for operating a drive control device, a facility with means for executing the method and a drive control device with such a facility.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
In many applications, for a converter drive with a DC link circuit, referred to here and below in general terms as a drive control device, because of so-called harmonics a DC link ripple voltage arises. If for example the DC link circuit is fed from an uncontrolled diode bridge from the three-phase alternating current network, the DC link circuit voltage is periodically stationary and contains the multiples of six times the network supply frequency. In addition, for unsymmetrical networks further harmonics (e.g. twice the network supply frequency) can also be contained therein.
A ripple in the DC link circuit voltage generates subharmonics in the motor voltage and in the motor current depending on the output frequency of a pulse converter when the influence of the DC link voltage cannot be compensated for by the activation method. This is the case for example during an overload or during a non-ideal compensation by temporal delay of the voltage measurement. Especially critical are output frequencies in which the frequency of the subharmonics arising is small or even becomes a zero-frequency quantity. In this case the voltage harmonics generate high harmonic content in the output currents which have a negative effect on the regulation, the quality of the torque and the load on the inverter.
Previously the problem of undesired subharmonics was solved by the degree of control for critical output frequencies being reduced far enough for a majority of the subharmonics to be able to be avoided by compensation of the DC link circuit voltage. This leads however to a lower utilization of the converter, since in these ranges the maximum output voltage is no longer available. In addition it is not optimal with previous approaches that with a non-ideal compensation of the DC link circuit voltage, subharmonic content which has to be taken into account still remains in the linear range of the modulator.
It would therefore be desirable and advantageous to provide an improved method and a facility to obviate prior art shortcomings and to make it possible to reduce the undesired subharmonics.